96,927 research outputs found
Higher dimensional thin-shell wormholes in Einstein-Yang-Mills-Gauss-Bonnet gravity
We present thin-shell wormhole solutions in Einstein-Yang-Mills-Gauss-Bonnet
(EYMGB) theory in higher dimensions d\geq5. Exact black hole solutions are
employed for this purpose where the radius of thin-shell lies outside the event
horizon. For some reasons the cases d=5 and d>5 are treated separately. The
surface energy-momentum of the thin-shell creates surface pressures to resist
against collapse and rendering stable wormholes possible. We test the stability
of the wormholes against spherical perturbations through a linear
energy-pressure relation and plot stability regions. Apart from this restricted
stability we investigate the possibility of normal (i.e. non-exotic) matter
which satisfies the energy conditions. For negative values of the Gauss-Bonnet
(GB) parameter we obtain such physical wormholes.Comment: 9 pages, 6 figures. Dedicated to the memory of Rev. Ibrahim Eken
(1927-2010) of Turke
TetSplat: Real-time Rendering and Volume Clipping of Large Unstructured Tetrahedral Meshes
We present a novel approach to interactive visualization and exploration of large unstructured tetrahedral meshes. These massive 3D meshes are used in mission-critical CFD and structural mechanics simulations, and typically sample multiple field values on several millions of unstructured grid points. Our method relies on the pre-processing of the tetrahedral mesh to partition it into non-convex boundaries and internal fragments that are subsequently encoded into compressed multi-resolution data representations. These compact hierarchical data structures are then adaptively rendered and probed in real-time on a commodity PC. Our point-based rendering algorithm, which is inspired by QSplat, employs a simple but highly efficient splatting technique that guarantees interactive frame-rates regardless of the size of the input mesh and the available rendering hardware. It furthermore allows for real-time probing of the volumetric data-set through constructive solid geometry operations as well as interactive editing of color transfer functions for an arbitrary number of field values. Thus, the presented visualization technique allows end-users for the first time to interactively render and explore very large unstructured tetrahedral meshes on relatively inexpensive hardware
Multi-scale space-variant FRep cellular structures
Existing mesh and voxel based modeling methods encounter difficulties when dealing with objects containing cellular structures
on several scale levels and varying their parameters in space. We describe an alternative approach based on using real functions evaluated procedurally at any given point. This allows for modeling fully parameterized, nested and multi-scale cellular
structures with dynamic variations in geometric and cellular properties. The geometry of a base unit cell is defined using Function Representation (FRep) based primitives and operations. The unit cell is then replicated in space using periodic
space mappings such as sawtooth and triangle waves. While being replicated, the unit cell can vary its geometry and topology due
to the use of dynamic parameterization. We illustrate this approach by several examples of microstructure generation within a given volume or
along a given surface. We also outline some methods for direct rendering and fabrication not involving auxiliary mesh and voxel
representations
Shape: A 3D Modeling Tool for Astrophysics
We present a flexible interactive 3D morpho-kinematical modeling application
for astrophysics. Compared to other systems, our application reduces the
restrictions on the physical assumptions, data type and amount that is required
for a reconstruction of an object's morphology. It is one of the first publicly
available tools to apply interactive graphics to astrophysical modeling. The
tool allows astrophysicists to provide a-priori knowledge about the object by
interactively defining 3D structural elements. By direct comparison of model
prediction with observational data, model parameters can then be automatically
optimized to fit the observation. The tool has already been successfully used
in a number of astrophysical research projects.Comment: 13 pages, 11 figures, accepted for publication in the "IEEE
Transactions on Visualization and Computer Graphics
Procedural function-based modelling of volumetric microstructures
We propose a new approach to modelling heterogeneous objects containing internal volumetric structures with size of details orders of magnitude smaller than the overall size of the object. The proposed function-based procedural representation provides compact, precise, and arbitrarily parameterised models of coherent microstructures, which can undergo blending, deformations, and other geometric operations, and can be directly rendered and fabricated without generating any auxiliary representations (such as polygonal meshes and voxel arrays). In particular, modelling of regular lattices and cellular microstructures as well as irregular porous media is discussed and illustrated. We also present a method to estimate parameters of the given model by fitting it to microstructure data obtained with magnetic resonance imaging and other measurements of natural and artificial objects. Examples of rendering and digital fabrication of microstructure models are presented
Electroweak corrections to hadronic event shapes and jet production in e+e- annihilation
We present a complete calculation of the electroweak O(alpha^3 alpha_s)
corrections to three-jet production and related event-shape observables at
electron--positron colliders. The Z-boson resonance is described within the
complex-mass scheme, rendering the calculation valid both in the resonance and
off-shell regions. Higher-order initial-state radiation is included in the
leading-logarithmic approximation. We properly account for the corrections to
the total hadronic cross section and for the experimental photon isolation
criteria. To this end we implement contributions of the quark-to-photon
fragmentation function both in the slicing and subtraction formalism. The
effects of the electroweak corrections on various event-shape distributions and
on the three-jet rate are studied. They are typically at the few-per-cent
level, and remnants of the radiative return are found even after inclusion of
appropriate cuts.Comment: 47 pages, 20 figure
Multi-dimensional models of circumstellar shells around evolved massive stars
Massive stars shape their surrounding medium through the force of their
stellar winds, which collide with the circumstellar medium. Because the
characteristics of these stellar winds vary over the course of the evolution of
the star, the circumstellar matter becomes a reflection of the stellar
evolution and can be used to determine the characteristics of the progenitor
star. In particular, whenever a fast wind phase follows a slow wind phase, the
fast wind sweeps up its predecessor in a shell, which is observed as a
circumstellar nebula. We make 2-D and 3-D numerical simulations of fast stellar
winds sweeping up their slow predecessors to investigate whether numerical
models of these shells have to be 3-D, or whether 2-D models are sufficient to
reproduce the shells correctly. We focus on those situations where a fast
Wolf-Rayet (WR) star wind sweeps up the slower wind emitted by its predecessor,
being either a red supergiant or a luminous blue variable. As the fast WR wind
expands, it creates a dense shell of swept up material that expands outward,
driven by the high pressure of the shocked WR wind. These shells are subject to
a fair variety of hydrodynamic-radiative instabilities. If the WR wind is
expanding into the wind of a luminous blue variable phase, the instabilities
will tend to form a fairly small-scale, regular filamentary lattice with thin
filaments connecting knotty features. If the WR wind is sweeping up a red
supergiant wind, the instabilities will form larger interconnected structures
with less regularity. Our results show that 3-D models, when translated to
observed morphologies, give realistic results that can be compared directly to
observations. The 3-D structure of the nebula will help to distinguish
different progenitor scenarios.Comment: Accepted for publication in A&A. All figures in low resolution. v2:
language corrections and addition of DOI numbe
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